Plasma addressed liquid crystal display with glass spacers

ABSTRACT

A flat display device, preferably of the PALC type, in which the plasma channels are formed by etching laterally-spaced slots in a spacer plate, attaching a thin dielectric sheet over the etched spacer plate, and bonding the etched spacer plate to a transparent substrate such that each channel is formed by the portion of the substrate between flanking walls formed by the etched slots in the spacer plate, adjacent flanking walls in the spacer plate, and the overlying portion of the thin dielectric sheet. In a modification, strengthening crossbars are formed between adjacent flanking walls.

RELATED APPLICATIONS

[0001] 1) Application, Ser. No. 08/______, filed (5604-0381

[0002] 2) Application, Ser. No. 08/______, filed (5604-0382).

[0003] 3) Application, Ser. No.______, filed (5604-0394).

BACKGROUND OF INVENTION

[0004] This invention relates to plasma channels, to display devicescomprising plasma channels, and to plasma-addressed liquid crystaldisplay panels commonly referred to as “PALC” display devices using suchchannels. PALC devices comprise, typically, a sandwich of: a firstsubstrate having deposited on it parallel transparent column electrodes,commonly referred to as “ITO” columns or electrodes since indium-tinoxides are typically used, on which is deposited a color filter layer; asecond substrate comprising parallel sealed plasma channelscorresponding to rows of the display crossing all of the ITO columns andeach of which is filled with a low pressure ionizable gas, such ashelium, neon and/or argon, and containing spaced cathode and anodeelectrodes along the channel for ionizing the gas to create a plasma,which channels are closed off by a thin transparent dielectric sheet;and a liquid crystal (LC) material located between the substrates. Thestructure behaves like an active matrix liquid crystal display in whichthe thin film transistor switches at each pixel are replaced by a plasmachannel acting as a row switch and capable of selectively addressing arow of LC pixel elements. In operation, successive lines of data signalsrepresenting an image to be displayed are sampled at column positionsand the sampled data voltages are respectively applied to the ITOcolumns. All but one of the row plasma channels are in the de-ionized ornon-conducting state. The plasma of the one ionized selected channel isconducting and, in effect, establishes a reference potential on theadjacent side of a row of pixels of the LC layer, causing each LC pixelto charge up to the applied column potential of the data signal. Theionized channel is turned off, isolating the LC pixel charge and storingthe data voltage for a frame period. When the next row of data appearson the ITO columns, only the succeeding plasma channel row is ionized tostore the data voltages in the succeeding row of LC pixels, and so on.As is well known, the attenuation of the backlight or incident light toeach LC pixel is a function of the stored voltage across the pixel. Amore detailed description is unnecessary because the construction,fabrication, and operation of such PALC devices have been described indetail in the following U.S. patents and publication, the contents ofwhich are hereby incorporated by reference: U.S. Pat. Nos. 4,896,149;5,077,553; 5,272,472; 5,276,384; and Buzak et al., “A 16-Inch Full ColorPlasma Addressed Liquid Crystal Display”, Digest of Tech. Papers, 1993SID Int. Symp., Soc. for Info. Displ. pp. 883-886.

[0005] A partial perspective view of the PALC display described in the1993 SID Digest is shown in FIG. 2. The method described in thereferenced publication for making the plasma channels is to chemicallyetch a flat glass substrate to form parallel semi-cylindrically shapedrecesses defined by spaced ridges or mesas and to bond on top of themesas a thin dielectric cover sheet having a thickness in the range ofabout 30-50 μm.

[0006] The above construction and its fabrication encounters certainproblems. Since the channel electrodes must be patterned on the slopingsidewall of the channel, the dimensions and placement of the electrodescannot be accurately controlled. Moreover, since slight variations inprocessing conditions can alter the etch rate, the channel etchingprocess is difficult to control; hence the depth of the channel, whichis dependent on control of the etching process, is difficult to control.

[0007] European Patent 0 500 084 A2 describes the formation of channelsby patterning of electrodes on a flat substrate, providing spacers onthe flat substrate, and placing the thin glass sheet on top of thespacers. The discharge space thus extends continuously across theelectrodes. However, the continuous discharge space will lead betweenchannels to crosstalk which is difficult to avoid. Moreover, the spacershave to be formed on the flat substrate by deposition and/or etchingprocesses, such as screen printing. Since the spacers have to be asthick as the required channel depth (˜100 microns or more) thefabrication of the spacers adds complexity to the process.

[0008] European Patents 0 500 085 A2 and 0554 851 A1 describe theformation of channels by screen printing partition walls. However, thisis also a difficult process, which may require multiple coats to obtainthe required wall height.

SUMMARY OF INVENTION

[0009] An object of the invention is an improved channel plate.

[0010] A further object of the invention is an improved plasma-addresseddisplay device.

[0011] Another object of the invention is an improved method forfabricating the plasma channels of a PALC display device.

[0012] In accordance with a first aspect of the invention, a channelplate comprises a dielectric substrate and a thin dielectric sheet-likemember arranged over and spaced from the substrate by a plurality oflaterally spaced, channel-defining spacer members each formed as part ofa dielectric sheet patterned by through-holes, which latter sheet isherein referred to as the spacer sheet or plate. The holes areconfigured to form the desired channel configurations, typicallyelongated parallel channels, which preferably are straight but whichalso may be curved while still maintaining a substantially parallelrelationship. The height of the spacer sheet above the substratedetermines the height of the channels, which are each formed by theportion of the substrate surface extending between adjacent flankingspacers, the flanking spacers themselves forming the channel walls, andthe overlying portion of the thin dielectric sheet-like member. Spacedelectrodes are provided in each channel as well as a plasma-formingatmosphere. The channels are formed when the three sheet-likemembers—the substrate, the spacer plate, and the thin dielectricsheet—are assembled and bonded together.

[0013] In accordance with a second aspect of the invention, thepatterning of the spacer sheet is such as to provide strengtheningcrossbars extending preferably transverse to and between adjacent spacermembers. The crossbars may have a different height than that of thespacers.

[0014] In accordance with a first preferred embodiment of the invention,the substrate is of glass, the thin dielectric sheet is of glass, andthe spacer sheet is a glass plate, with the through-holes in the form ofslots made by chemical or plasma etching or by mechanical means such assandblasting. The three glass members may be bonded together using fusedglass frit as described in several of the cited patents andpublications, or by anodic bonding as described in the first relatedpatent application identified above.

[0015] In accordance with a another preferred embodiment of theinvention, the channel plate is part of a PALC display device, and thecombination of the substrate, patterned spacer plate and the overlyingthin dielectric sheet-like member, together with the electrodesconstitutes the plasma channels or channel plate of the PALC displaydevice.

[0016] The various features of novelty which characterize the inventionare pointed out with particularity in the claims annexed to and forminga part of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated and described the preferredembodiments of the invention, like reference numerals or letterssignifying the same or similar components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the drawings:

[0018]FIG. 1 is a schematic block diagram of a conventional flat paneldisplay system;

[0019]FIG. 2 is a perspective view of part of a conventional PALCdisplay device;

[0020]FIG. 3 is a perspective view of a part of one form of a channelplate according to the invention for use in a PALC color display, andFIG. 4 is a top view of the spacer plate used in that channel plate;

[0021]FIG. 5 is an exploded side view of the channel plate of FIG. 3;

[0022]FIGS. 6 and 7 are schematic views indicating two different ways ofetching the spacer plate used in the embodiments of FIGS. 3-5;

[0023]FIGS. 8 and 9 are side and top views, respectively, of part ofanother form of spacer plate for use in another embodiment in accordancewith the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0024]FIG. 1 shows a flat panel display system 10, which represents atypical PALC display device ahd the operating electronic circuitry. Withreference to FIG. 1, the flat panel display system comprises a displaypanel 12 having a display surface 14 that contains a pattern formed by arectangular planar array of nominally identical data storage or displayelements 16 mutually spaced apart by predetermined distances in thevertical and horizontal directions. Each display element 16 in the arrayrepresents the overlapping portions of thin, narrow electrodes 18arranged in vertical columns and elongate, narrow channels 20 arrangedin horizontal rows. (The electrodes 18 are hereinafter referred to fromtime to time as “column electrodes”). The display elements 16 in each ofthe rows of channels 20 represent one line of data.

[0025] The widths of column electrodes 18 and channels 20 determine thedimensions of display elements 16, which are typically of rectangularshape. Column electrodes 18 are deposited on a major surface of a firstelectrically nonconductive, optically transparent substrate 34 (FIG. 2),and the channel rows are usually built into a second transparentsubstrate 36. Skilled persons will appreciate that certain systems, suchas a reflective display of either the direct view or projection type,would require that only one substrate be optically transparent.

[0026] Column electrodes 18 receive data drive signals of the analogvoltage type developed on parallel output conductors 22′by differentones of output amplifiers 23 (FIG. 2) of a data driver or drive circuit24, and channels 20 receive data strobe signals of the voltage pulsetype developed on parallel output conductors 26′by different ones ofoutput amplifiers 21 (FIG. 2) of a data strobe or strobe means or strobecircuit 28. Each of the channels 20 includes a reference electrode 30(FIG. 2) to which a reference potential, such as ground, common to eachchannel 20 and data strobe 28 is applied.

[0027] To synthesize an image on the entire area of display surface 14,display system 10 employs a scan control circuit 32 that coordinates thefunctions of data driver 24 and data strobe 28 so that all columns ofdisplay elements 16 of display panel 12 are addressed row by row in rowscan fashion as had been described. Display panel 12 may employelectro-optic materials of different types. For example, if it uses suchmaterial that changes the polarization state of incident light rays,display panel 12 is positioned between a pair of light polarizingfilters, which cooperate with display panel 12 to change the luminanceof light propagating through them. The use of a scattering liquidcrystal cell as the electro-optic material would not require the use ofpolarizing filters, however. All such materials or layer of materialswhich attenuate transmitted or reflected light in response to thevoltage across it are referred to herein as electro-optic materials. AsLC materials are presently the most common example, the detaileddescription will refer to LC materials but it will be understood thatthe invention is not limited thereto. A color filter (not shown) may bepositioned within display panel 12 to develop multi-colored images ofcontrollable color intensity. For a projection display, color can alsobe achieved by using three separate monochrome panels 12, each of whichcontrols one primary color.

[0028]FIG. 2 illustrates the PALC version of such a flat display panelusing LC material. Only 3 of the column electrodes 18 are shown. The rowelectrodes 20 are constituted by a plurality of parallel elongatedsealed channels underlying (in FIG. 2) a layer 42 of the LC material.Each of the channels 20 is filled with an ionizable gas 44, closed offwith a thin dielectric sheet 45 typically of glass, and contains on aninterior channel surface first and second spaced elongated electrodes30, 31 which extend the full length of each channel. The first electrode30 is grounded and is commonly called the anode. The second electrode 31is called the cathode, because to it will be supplied relative to theanode electrode a negative strobe pulse sufficient to cause electrons tobe emitted from the cathode 31 to ionize the gas. As explained above,each channel 20, in turn, has its gas ionized with a strobe pulse toform a plasma and a grounded line connection to a row of pixels in theLC layer 42 above. When the strobe pulse terminates, and afterdeionization has occurred, the next channel is strobed and turned on.Since the column electrodes 18 each cross a whole column of pixels,typically only one plasma row connection at a time is allowed on toavoid crosstalk.

[0029] Fabrication of a PALC device is typically done as described inthe 1993 SID digest paper by providing first and second substrates 34,36 with the first substrate 34 comprising a glass panel on which isdeposited the ITO column electrodes 18, followed by color filterprocessing over the ITO electrodes to produce the RGB stripes (notshown), followed by the black surround processing and liquid crystalalignment processing. The second substrate 36, also a glass panel, ismasked and etched to form the channels 20, following which the plasmaelectrode material is deposited and masked and etched to form thecathode 31 and anode 30 electrodes. A thin dielectric glass microsheet45 is then sealed across the peripheral edges of the device to form withthe ridges 50 the channels 20, which are then exhausted, back-filledwith a low-pressure ionizable gas such as helium and/or neon andoptionally with a small percentage of other noble gases and sealed off.LC alignment of the exposed surface of the microsheet 45 is then carriedout. The two assembled substrates are then assembled into a panel withthe two LC alignment surfaces spaced apart and facing, the LC material42 introduced into the space, and electrical connections made to thecolumn electrodes 18 and plasma electrodes 30, 31.

[0030]FIG. 3 is a perspective view of part of one form of channel plate52 in accordance with the invention for one form of liquid crystaldisplay panel in accordance with the invention. A thick flat glassbottom plate 36 forms a substantially transparent dielectric substratefor the plasma channels 20. Over the bottom plate 36 is deposited spacedelectrode layer portions 30, 31.

[0031] In accordance with the invention, the channels walls are formedin a transparent dielectric sheet 50 substantially equal in thickness tothe required channel depth. The dielectric sheet 50 is preferably of anetchable material, such as glass. This is accomplished with glass byetching through-holes 52 in the glass using conventional masking andetching processes as shown in FIG. 4.

[0032]FIGS. 6 and 7 illustrate two preferred ways for etching the glassto make the hole walls as close to the vertical as possible. This can bedone as shown in FIG. 6 by starting with a relatively small opening 54in an etch mask 56 and etching a hole 58 whose lateral dimensions are atleast five times larger than mask opening 54 and the depth of the hole,in this case the thickness of the sheet 50. The dashed lines show theetched profiles of the sidewalls using an isotropic etchant during theetching process. It can be seen that, as the etching progresses, thesidewalls become steeper. The larger the lateral dimensions of theetched hole 58 relative to the thickness of the glass sheet 50, thesteeper the sidewalls. As an example, not meant to be limiting, for aglass sheet 50 of about 100 μm thick, to etch holes that are 500 μmwide, the mask hole 54 is preferably 100 μm wide. For a panel withstraight channels as illustrated in FIG. 2, the holes 52 would beelongated slots extending nearly the full length of the plate 50, butwould terminate at opposite sides in an annular glass border region 53so that the plate 50 remains as an integral element except for the holes52 in the form of parallel slots spaced apart by spacer walls 58.

[0033]FIG. 7 shows an etching modification in which the spacer walls canbe made even more vertical by carrying out the etching from both sidesof the plate 50. In this case, etch masks 56 are required on both sidesof the plate except where the holes 58 are to be formed, and the maskholes 54 overlie one another. The dashed lines that show the etchingprofiles as the etching progresses shows that for a double-sided etchingprocess, the sidewalls can be even steeper than with the single-sidedetching process shown in FIG. 6.

[0034] The thickness of the channel sidewalls 58 thus produced, it willbe appreciated, represents the height of the channels 20 and constitutethe spacers that space the thin dielectric sheet 45 that closes off thechannels from the substrate 36, and thus the reference to the aperturedplate 50 as the spacer plate. The etching can be by conventionalchemical etchants or by conventional plasma etching. Alternatively, amechanical erosion process can be substituted, such as sandblasting.This may be less costly and could also be used for materials for thespacer plate 50 that are more difficult to etch.

[0035] The channel electrodes 30, 31 are separately deposited andpatterned on the substrate 36 as described in the referenced papers andpatents, after which the thin glass sheet 45 is attached over theapertured spacer plate 50, and the latter then aligned and attached tothe substrate 36 containing the electrodes. As shown, by positioning thespacer plate wails 58 over the electrodes 30, 31, then adjacent channels20 would share an electrode which would reduce the number of electrodesrequired. The walls 58 are shown with a slightly tapered shape, whichwould follow if the single-sided etching technique were used, as theglass surfaces closer to the mask hole 54 would etch more than the moreremote glass portions. If the double-sided etching process were used,then a double taper would result.

[0036] The attaching of the thin dielectric sheet 45 to the spacer plate50, and the attaching of the spacer plate 50 to the substrate 36 can becarried out using fused glass frit at the periphery of the structure.Alternatively, anodic bonding can be used. Anodic bonding as such is awell known process for bonding two flat surfaces of ion-containingmaterials, such as glass. In a typical process, the glass sheets areplaced against each other and an electric field applied across themwhile heating them to some intermediate elevated temperature whichallows glass ions to become mobile. The ions migrate to the interfacebetween the two sheets and pulls them together. The resultant force, inthe presence of heat, leads to the formation of a permanent bond betweenthe two sheets. Typical temperatures are much lower than the softeningtemperature of the glass. The glass frit seal will only be necessary inthe electrode area after attaching the thin sheet 45.

[0037] The resultant assembled channel plate structure 52 is shown inFIG. 3. The remainder of the PALC panel can be fabricated in the usualway by filling and sealing the plasma panel and then forming the LC partof the panel on top of the thin glass sheet 45 as shown in FIG. 5 in anexploded view. The upper plate 34 may have deposited spacer members 60which are aligned with the spacer walls 58 and act to space apart theupper structure 34 with its ITO electrodes 18 from the glass sheet 45 toprovide a confined space for the LC material.

[0038] In a variation of the invention, where the width of the channels20 may be large, it may be desirable to increase the mechanical strengthof the spacer plate. This can be done by etching strengthening crossbarsin a spacer plate 62. This is illustrated in FIGS. 8 and 9 at 62. Thecrossbars 64 which extend laterally to and between the spacer walls 58are thus integral with the plate 62. To avoid the crossbars 64 frompossibly detrimentally affecting the operation of the plasma dischargein the channels 20, their height can be reduced without reducing theheight of the spacer walls 58. In the embodiment shown, the height h ofthe crossbars 64 is reduced from the top. The height h can be controlledby the width of the etching opening in the etch mask and the degree ofthe overetching. By appropriate masking and etching techniques, easilydetermined by those skilled in this art, the crossbars 64 can be made sothat they do not extend all the way to the height of the channels 20.

[0039] The broken lines at the edges of the elements in the figuresindicate that what is shown is a small section broken off from a largerassembly, since, as will be appreciated, typically a PALC display devicefor monitor use would contain several hundred column electrodes 18 andseveral hundred plasma channels 20.

[0040] It will be noted that the spacer wall portions 58 do not overlapor cover the sides of the electrically conductive layers 30, 31, whichthus remain exposed and able to perform their function of igniting anelectrically conductive plasma when suitable voltages are appliedbetween them. The electrode materials are typically of a metal such ascopper, or layers of Cu—Cr—Cu, or other suitable metals.

[0041] All of the methods described in the referenced patents andpublication will be suitable for making the remaining parts of the panelof the invention.

[0042] The invention is generally applicable to all kinds of flatdisplays, and in particular to displays of the plasma-addressed type,especially PALC displays that typically have a small channel pitch foruse in computer monitors, workstations or TV applications. While themain application of the channel plate of the invention is in PALC typedisplay devices, the same plasma plate construction 52 can also be usedas a plasma display device where the output is the light, generated bythe plasma, which can exit the device via the transparent substrateand/or the overlying transparent sheet-like member.

[0043] Several preferred examples for the FIG. 3 embodiment are (allvalues are in μm): a wall width of about 20-50; a wall height of about50-160; and a wall pitch of about 200-500.

[0044] It will be appreciated that the drawing figures are not to scaleand in particular the channel widths have been exaggerated to show theelectrodes.

[0045] Still further, while the channels in the substrate are typicallystraight, the invention is not limited to such a configuration and otherchannel shapes, such as a meandering shape, are also possible within thescope of the invention.

[0046] While the invention has been described in connection withpreferred embodiments, it will be understood that modifications thereofwithin the principles outlined above will be evident to those skilled inthe art and thus the invention is not limited to the preferredembodiments but is intended to encompass such modifications.

What is claimed is:
 1. A channel plate for a flat display comprisingelongated channels on a dielectric substrate and electrode surfaces ineach of the channels, said dielectric substrate comprisingchannel-defining flanking wall portions on the substrate with a thindielectric sheet-like member over the flanking wall portions,characterized in that: a) the flanking wall portions are parts of anintegral dielectric sheet.
 2. A channel plate as claimed in claim 1 ,wherein the dielectric sheet is constituted of glass.
 3. A channel plateas claimed in claim 1 , wherein the flanking wall portions are joined attheir periphery by an integral border region.
 4. A channel plate asclaimed in claim 1 , wherein the flanking wall portions are laterallyspaced apart by etched slots.
 5. A channel plate as claimed in claim 1 ,wherein the flanking wall portions seat on top of the electrodesurfaces.
 6. A channel plate as claimed in claim 1 , wherein spacedcrossbars extend laterally between flanking wall portions.
 7. A channelplate as claimed in claim 6 , wherein the crossbars have a smallerheight than that of the flanking wall portions.
 8. A plasma channelplate for use in a PALC display device comprising elongated channelshaving electrodes and filled with a plasma-forming atmosphere on asubstantially transparent dielectric substrate, characterized in that:a) on the substrate is a plurality of deposited spaced electricallyconductive electrode layer portions, b) each of the channels is definedby flanking wall portions formed as part of an integral spacer platemounted over the substrate and over the spacer plate a thin dielectricsheet.
 9. A plasma channel plate as claimed in claim 8 , wherein thesubstrate, the spacer plate, and the thin dielectric sheet are eachconstituted by a glass sheet-like member.
 10. A plasma channel plate asclaimed in claim 9 , wherein the walls have a width of about 20-50 μm, aheight of about 50-160 μm, and a pitch of about 200-500 μm.
 11. Achannel plate as claimed in claim 8 , wherein spaced crossbars extendlaterally between flanking wall portions.
 12. A channel plate as claimedin claim 8 , wherein the crossbars have a smaller height than that ofthe flanking wall portions.
 13. A plasma-addressed display devicecomprising a layer of electro-optical material between a first substratecomprising data electrodes and a channel plate as claimed in claim 8 .14. In a method for making a channel plate for a flat display device,said method being characterized in that: (a) providing a substantiallytransparent dielectric substrate, (b) providing a substantiallytransparent spacer plate having first and second opposed surfaces, (c)forming in the spacer plate a plurality of substantially equally-spacedwalls each having a height equal to the thickness of the spacer platebetween the first and second surfaces, (d) bonding a thin dielectricsheet over the first surface of the spacer plate, (e) depositing anelectrically conductive material over the substrate to form on thesubstrate spaced electrode layer portions, (f) bonding the spacer platevia its second surface to the substrate with the spaced walls extendinggenerally transverse to the substrate and such that spaced electrodeportions are located between each adjacent pair of walls.
 15. The methodof claim 14 , wherein the substrate, the spacer plate, and the thindielectric sheet are made of glass.
 16. The method of claim 14 , whereinstep (c) is carried out by chemically or plasma etching slots in thespacer plate.
 17. The method of claim 14 , wherein step (c) is carriedout by chemically etching the spacer plate using an etch mask withopenings having a smaller width than the spacing between the spacerplate walls.
 18. The method of claim 14 , wherein step (c) is carriedout by mechanically eroding slots between the spacer plate walls. 19.The method of claim 14 , wherein spaced crossbars are formed in thespacer plate so as to extend laterally between flanking wall portions.20. The method of claim 19 , wherein the crossbars have a smaller heightthan that of the flanking wall portions.
 21. The method of claim 14 ,wherein the bonding steps are carried out by glass frit or anodicbonding.
 22. In a method for making the plasma channel plate of aplasma-addressed electro-optic display device comprising a layer ofelectro-optic material, data electrodes coupled to the electro-opticlayer and adapted to receive data voltages for activating portions ofthe electro-optic layer, a plurality of elongated plasma channelsextending generally transverse to the data electrodes for selectivelyswitching on said electro-optic portions, and a dielectric sheet closingoff the plasma channels on the side facing the data electrodes, saidplasma channels each comprising spaced elongated cathode and anodeplasma electrodes and an ionizable gas filling, said method beingcharacterized in that: (a) providing a substantially transparentdielectric substrate, (b) providing a substantially transparentdielectric spacer plate having first and second opposed surfaces, (c)forming by etching in the spacer plate a plurality of substantiallyequally-spaced walls each having a height equal to the thickness of thespacer plate between the first and second surfaces, (d) bonding a thindielectric sheet over the first surface of the spacer plate, (e)depositing an electrically conductive material over the substrate toform on the substrate spaced cathode and anode electrode layer portions,(f) bonding the spacer plate via its second surface to the substratewith the spaced walls extending generally transverse to the substrateand such that spaced electrode portions are located between eachadjacent pair of walls.
 23. In the method for making the plasma channelplate of a plasma-addressed electro-optic display device as claimed inclaim 22 , wherein the cathode and anode electrode portions are widerthan the spaced walls and the spaced walls are located over the cathodeand anode electrode portions such that adjacent channels share anelectrode.